1. Field of the Invention
The present invention relates to a shift control apparatus for an automatic transmission of a motor vehicle.
2. Description of Related Art
There is known an automatic transmission of a motor vehicle whose change gear ratio is variable or which can be placed in a selected one of a plurality of gear positions. The vehicle automatic transmission of this type uses a shift control apparatus for changing the change gear ratio or gear position of the transmission according to a predetermined shift pattern, based on actual running conditions of the vehicle as represented by a throttle opening angle (engine load) and a vehicle speed, for example.
In the shift control apparatus for the automatic transmission of the motor vehicle as described above, however, the change gear ratio or gear position is uniformly changed using the predetermined shift pattern, and the obtained gear ratio or gear position does not always match what the driver intends or wishes to achieve.
In view of the above problem, a shift control apparatus has been proposed which determines that the driver wishes to establish a SPORTY DRIVE mode if the rate of change of the throttle opening angle becomes equal to or higher than a predetermined value, and switches from a NORMAL (MEDIUM) MODE shift pattern to a SPORTY MODE shift pattern. Upon a lapse of a predetermined time after the switching, the shift control apparatus cancels shift control using the SPORTY MODE shift pattern and resumes shift control using the NORMAL (MEDIUM) MODE shift pattern. This type of shift control apparatus is disclosed in laid-open Publication No. 3-117773 of unexamined Japanese Patent Application, for example.
In the shift control technology disclosed in the above-identified publication, however, the shift control using the SPORTY MODE shift pattern is uniformly or invariably changed back to the shift control using a predetermined shift pattern, such as the MEDIUM MODE shift pattern, upon a lapse of the predetermined time after the normal shift control using the predetermined (MEDIUM MODE) shift pattern is switched to the SPORTY MODE shift control using the SPORTY MODE shift pattern. Accordingly, the transmission may be unexpectedly shifted up when the normal shift control is resumed, regardless of the driver's operations to drive the vehicle, thus making the driver feel uncomfortable or disagreeable due to the unexpected shift-up action.